This invention generally relates to gas turbine engines, and more particularly to a stator vane assembly having an extended fillet.
Gas turbine engines include high and low pressure compressors to provide compressed air for combustion within the engine. Both the high and low pressure compressors typically include multiple rotor discs. Stator vanes extend between each rotor disc along a compressor axis. Many gas turbine engine compressors include variable stator vanes which rotate about an axis which is transverse to the compressor axis. The rotation of the variable stator vanes about their axis regulates air flow and the compression of air within the compressor of the gas turbine engine during combustion.
As illustrated in FIG. 1, a variable stator vane 11 typically includes buttons 13 defined at each end (only one end shown) of the stator vane 11, which support the stator vane 11 ends on their flow path sides, and support trunnions 15 about which the stator vanes 11 rotate on their sides. Due to the limited amount of space available in the engine casing, the diameter of the buttons 13 is limited and often prevents the button 13 from supporting an entire vane airfoil 17. Therefore, a portion of the vane airfoil 17 overhangs a button end 23 (i.e. a vane overhang portion 19). The buttons 13 are received within holes in a casing wall which accommodate the rotation of the variable stator vanes 11.
An intersection area 21 between a button end 23 and the overhang portion 19 of the vane airfoil 17 may be unsupported by the stiff button 13. This is because the intersection area 21 defined between the button 13 and the vane airfoil 17 is supported by a strengthening fillet 25 which does not extend entirely along the vane overhang portion 19. Typically, the fillet 25 is a constant radius fillet and extends just aft of the button end 23. Therefore, a stiff-to-soft transition area is created near the intersection area 21. As a result, the overhang portion 19 of the vane airfoil 17 is highly susceptible to high vibrations from bending, and is also susceptible to high stresses. Disadvantageously, the high vibrations and high stresses located at the intersection area 21 between the button end 23 and the overhang portion 19 of the vane airfoil 17 may cause cracking and failure of the stator vane 11.
Several variable stator vane designs are known which reduce the susceptibility of the stator vane to cracks from high vibrations and high stresses. One known stator vane assembly includes local thickening in the intersection area between the button end and the overhang portion of the vane airfoil. The local thickening includes a thickness increase extending both forward (into the button) and aft (into the overhanging portion of the vane) approximately 60% of the length defined by the overhang portion. The thickening is provided to reduce both the vane's flexibility and vibration and the local stress concentration associated with the intersection. However, this approach disturbs airflow locally and forces airflow to detour around the thickened area until the airflow reaches the optimal location on the vane airfoil surface. An efficiency loss may be associated with the diversion of the airflow and may result in an even greater efficiency loss where the airflow becomes separated from the vane airfoil surface. In addition, there is a weight penalty associated with the added material needed to locally thicken the intersection area.
A second attempt to reduce the local stress concentration factor at the intersection area between the button end and the overhang portion of the vane includes an airfoil surface which is cut away locally at the intersection into the span of the vane airfoil. The goal is to increase the minimum radius of any inside corner of the stator vane. This stator vane design creates a large hole through the vane airfoil and allows a large amount of air leakage from the pressure side to the suction side of the compressor, which causes significant efficiency losses.
Attempts to mitigate the aerodynamic performance losses associated with the known stator vane designs mentioned above have been made by varying the corner radius at the intersection area (i.e. providing a variable radius fillet). However, this may cause the producability of the part to become challenging if not impossible.
Accordingly, it is desirable to provide an improved variable stator vane assembly that is simple to manufacture and that provides improved efficiency and increase strength at the intersection area between the button end and the overhang portion of the stator vane.